1. Field of the Invention
The present invention relates to a pickup control device, optical disk apparatus and pickup control method for the same, and is directed, for example, to servo control for high-speed recording and reproduction of an optical disk.
2. Related Background Art
In recent years, as the speed of recording and reproducing of CD and DVD is increased, optical disk apparatuses in which the optical disk rotates at a rotational frequency close to the limit of the disk motor and pickup mechanism are being actively researched.
When an optical disk rotates at high speed, the effects of surface vibration and/or eccentricity, which are rotational components of the optical disk, become large. Accordingly, a rotation correction device is generally mounted on an optical disk apparatus.
With conventional rotation correction devices, however, before performing rotation correction, the level of disturbance signals produced during rotation must be once stored into a memory (calibration operation) without performing rotation correction. Therefore, the conventional rotation correction devices are not suitable for such cases as when a spindle motor whose rotational frequency changes gradually is controlled as with CLV control, or when data must be retrieved under a condition that high-speed rotation takes place suddenly.
More specifically, with the conventional control methods, in a control technique, such as CAV, where the rotational frequency is constant, correction operation using data once stored is possible in the whole range from the inner circumference to the outer circumference. However, in a control technique, such as CLV, where the rotational frequency changes gradually from the inner circumference to the outer circumference, if the calibration operation is not performed again, the rotation correction cannot be correctly performed. Also, when spindle-up is performed in the operation of drive etc., the rotational frequency increases gradually until high-speed rotation is achieved. Consequently, without performing a transition to the high-speed condition while updating the surface vibration data and/or eccentricity data stored in the memory, reproduction cannot be correctly performed. In either case, the correction of surface vibration and/or eccentricity must be stopped to perform calibration, thus involving a high risk of focus deviation or track jump taking place at this moment.